Most prior art breast pumps designed for extracting milk are concerned only with controlling the rate at which a negative pressure is applied to the breast and, in some cases, the amount of negative or vacuum pressure. However, the amount of milk volume obtained in response to a constant average suction is quite low compared to that obtained by a suckling infant.
Recently, breast pump systems have been introduced that use a constantly running positive displacement vacuum pump, sense and monitor the negative pressure or vacuum and open a valve in response to the sensed vacuum in excess of the vacuum limit in order to decrease the vacuum to a desired point. Such systems are complex, which reduces reliability, and costly, which discourages breast feeding.
Other conventional breast pump systems, see FIGS. 3 and 4, include a pump assembly 10 having a reciprocating piston assembly 20 driven by a reversible motor 14. A rolling diaphragm 22 is connected via circumferential tension at an inner end 24 to a center post 26 of the piston assembly 20 and at an outer end 28 captured between the piston housing 30 and the drive housing 32. The vent piston 34 includes, in FIG. 3, a vent 36 formed as a bore that extends from a distal end 38 (at the top wall 37) to a proximal end 40 disposed adjacent the lower end of a side wall 42 of the vent piston 34, and in FIG. 4, a vent 36 formed as a bore that extends through a side wall 42 of the vent piston 34 to a channel 44 formed around the center post 26. Both the vents 36 enable the pressure chamber 46 to communicate with a portion 48 of the diaphragm 22 adjacent to connection to the center post 26.
In theory, it was thought and desired that the portion 48 would overcome the circumferential tension when a slight positive pressure was generated in the pressure chamber 46 when the vent piston 34 was disposed adjacent a port formed in an end wall of the piston housing 30 (e.g., near maximum extension) and move or deflect in the direction of the threaded piston 50 to facilitate defining an intermittent passage to atmosphere every time the vent piston 34 reached near maximum extension from the drive screw 52. However, it was discovered through testing and operation that the portion 48 was not consistently moving or deflecting as desired and that the portion 48 was not moving at maximum extension of the piston assembly 20 in response to the slight positive pressure present in the pressure chamber 46 and/or the portion 48 was moving near the beginning of a vacuum retraction pull by the piston assembly 20 (in an opposite direction from what was desired) so that the desired vacuum is not achieved. In other words, the breast pump system was too closed or only somewhat intermittently openable to atmosphere resulting in painful constant increasing vacuum profiles or under vacuum profiles that take a considerable time to operate properly, raising distrust as to proper operation. As a result, the conventional breast pump system took on average at least 20-30 seconds to reach a consistent steady state pressure or vacuum recovery profile. Sometimes it would take longer and still further sometimes it would never reach the desired consistent steady state vacuum recovery profile.
FIG. 5 is a graph of pressure versus time, illustrating the conventional prior art breast pump system (as conceptually shown in FIG. 1 and including as pump assembly as shown in either FIG. 3 or FIG. 4) vacuum recovery profile. One will note that in concept nearly any breast pump system includes, as shown in FIG. 1, a pump assembly housing 54 (with the pump assembly 10 disposed within, but not shown in this FIG. 1), a pair of collection units 56 each connected via tubing to a single port of the pump assembly and including breast flanges 58. As shown in FIG. 5, neither of the flanges 58 experiences a quick vacuum recovery profile from a 0 mm Hg reading (i.e., atmospheric pressure), where the desired vacuum profile smoothly oscillates between 0 mm Hg and 200 mm Hg (for this testing purpose only, in practice the maximum vacuum is selectable by the user). Rather, one flange 58 experiences a weak but steadily increasing vacuum profile (i.e., the lower trace 60) and the other flange 58 experiences a weak, barely increasing vacuum profile (i.e., the upper trace 62). Usually, the lower trace 60 may stabilize at the desired or called for 200 mm Hg and the upper trace 62 will eventually match the vacuum recovery profile of the lower trace 60. However, a significant disadvantage is the discomfort of the nursing mother that discourages her from breast feeding with the unnecessary complications. Further, it has been commonly observed that the lower trace 60 and/or both traces 60, 62 may actually continue to increase the amount of vacuum until reaching a painful level (e.g., approximately 250-270 mm Hg) where the nursing mother must rest operation of the prior art device by deactivating the pump assembly and removing the flange. Thereafter, the entire process must start over, which most likely is a repeat of the vacuum recovery profile as shown in FIG. 5. Another situation where a quick vacuum recovery profile is desired is when there is an intermittent leak in the system. Obvious disadvantages are not only the discomfort and possible pain, but also the time delays and frustration and distrust with faulty operation.
Therefore, there is a need in the art for simple, reliable electrical breast pump and electrical breast pump system that quickly attains and maintains a desired setting regardless if starting anew, after a break or as a result of a system leak and that overcomes the disadvantages of the complex and unreliable prior art systems.